Colorado has two laws. One is against brandishing (which I do believe means holding the gun or other weapon in a state of readiness) and the other is menacing (making a weapon visible in public with the intent to scare someone).
I believe BM's actions were menacing. But two things are necessary: the menaced person must feel frightened (and perhaps no one was - perhaps the persons who saw BM with the gun thought he was ridiculous and not scary) and the person with the gun had to want to scare people (which of course, nearly everyone here has said they believed he was trying to do).
You can protect your property without a gun. In California, if a person trespasses and you meet them on your property with a gun, you are going to be booked (because we have laws against guns in public - they must be properly stored while out of your house and only taken out of their storage, ammunition stored separately, when you get to the gun range or the hunting territory).
It would be very interesting to know if BM's gun was loaded. I assume that the searchers thought it was. I think it's good they didn't demand the police enforce the law (it would likely have been a misdemeanor), as then it would look like LE was using every reason to harass BM, which they should not do.
You can't carry a gun at your shoulder without touching it. So he clearly was touching it and n possession of it. He didn't need to brandish it to run afoul of CO law.
Colorado’s Menacing Law: What You Need to Know
That link includes tips on how to defend against the charge.